Friction Stir Welding (FSW) is known to be employed increasingly in aeronautics and space engineering, in railway technology and in automobile construction. This simple, clean and innovative assembly method is distinguished by its high potential for automation and by dispensing with the requirement for rivets, the production costs being lowered and the weight of structures produced being reduced.
In friction-stir welding, as described, for example, in WO 93/10935, it is known to bring into contact, and hold in this position, two workpieces which are to be welded to one another. A welding rod or a rod-shaped projection of a corresponding tool is introduced with a rotational movement into the connection region of the workpieces, until a shoulder arranged on the tool above the welding rod lies on the surface of the workpieces. In this case, due to the relative movement between the tool and workpieces, frictional heat is generated, so that adjacent material regions in the connection region assume a plasticized state. While the rotating welding rod is in contact with the connection region, the tool is moved forwards along the connecting line of the workpieces, so that the material located around the welding rod is plasticized and subsequently consolidated. Before the material hardens completely, the welding rod is removed from the connection region or the workpieces. Due to the shoulder, which is in contact with the workpiece surface during welding, additional frictional heat is generated, and an escape of plasticized material can be prevented.
Materials, such as, for example, metals, their alloys, metal composite materials (what are known as MCCs) or suitable plastics, can be welded in this way as a butt joint, overlap-joint or T-joint connection. Of course, spot connections can also be generated, a forward movement of the welding rod which is in contact rotationally with the connection region or a relative translational movement between the rotating welding rod and workpieces being dispensed with.
However, the friction-stir technique is also employed in the repair, machining and finishing of workpieces and is usually designated as friction-stir processing. In this case, as described above, a rod-shaped projection is introduced with a rotational movement into at least one workpiece (that is to say, welding in solid occurs), in order to modify the workpiece material at least in the contact region of the welding rod. For repair purposes, the rotating welding rod is introduced, for example, into a crack of a workpiece, to name only one example of use.
The disadvantage of both friction-stir welding and friction-stir processing, however, is that welding or machining of curved components, in particular spherical components, has not been possible hitherto beyond special radii, since the shoulder can no longer be supported or, in the case of a concave component surface, lies above the assembly point. The same applies to the production of orbital seams, such as generated, for example, in the connection of pipes, half-shells or hemispheres. It has likewise not been possible hitherto to weld or machine components having any other surface contour (for example, with angular clearances).